Polyphase motor speed control



NOV. 29, 1955 H, s JACQBS 2,725,511

POLYPHASE MOTOR SPEED CONTROL Original Filed April 16, 1945 BY MW @H74United StatesPatent t,

POLYPHASE MOTOR SPEED CONTROL Henry S. Jacobs, Milwaukee, Wis., assignorto Harnischfeger Corporation, Milwaukee, Wis., a corporation ofWisconsin 2 Claims. (Cl. S18-202) This invention relates to alternatingcurrent electric motor control and resides in an apparatus wherein themotor under operation remains permanently connected to a power sourceand the output of the motor is varied by alteration of the inductivereactance of control windings disposed iu the motor circuit throughregulation of exciting currents acting to alter the magnitude ofmagnetic ux disposed in paths linked with said control windings theexciting currents being derived if desired from rectiers supplied byreactively regulatable sources of alternating current.

This application is a division of my co-pending application bearingSerial Number 588,685, led on April 16, 1945, now Patent No. 2,559,538,and relates to that part of my invention pertaining to the speedregulation of alternating current motors.

Inaccordance with the present invention speed control l and reversalthrough application of regulated voltage of the desired phase sequenceto the input terminals of a motor is provided by inductive or reactiveregulation of the motor circuits, permitting control of speed in eitherdirection under suitable load conditions over a wide smooth steplessrange without the need for resort to separation or engagement of switchcontacts. Such control may be manipulated through the employment ofsimple manual means.

Inductively reactive circuit components have heretofore found use in thecontrol 'of alternating current motors by introduction of the same intothe motor primary circuits as a substitute for switching. The use ofsuch circuits has facilitated automatic control systems and applicationsthereof have usually been interdependent with special regulatingelements. Such control systems, however,`have required the unbalancingof circuit conditions with resulting asymmetrical voltage relations atthe motor terminals and uneven distribution of load on the power lines.Also, there has been resort to single phasing of the4 m'otor and to suchcomplications as phase shifting to provide` the desired results.

It is an object of this invention to provide a swit'chless inductiveregulation for control of a polyphase alternating current motor thatwill provide for reversal in rotation and for speed control undersuitable load conditions and yet maintain a balanced load upon the powerlines for all conditions of operation and which will retainasymmetricalvoltage relationship at the motor terminals.

It is another object of this invention to effectively join each of thepower leads that form a portion of the control circuit to but one motorterminal for a given direction of rotation and to alter the eltectiveconnection of some of the power leads to other of the motor terminalsfor reversal of rotation yby employment of inductive impedances that actto diminish current values to negligible amounts incertain power leadsin response to a manual regulator that `acts to alternativelyy affectthe impedance values.

It'is a further object of this invention to provide switchless inductiveor reactive control of circuit conditions in the secondary circuit ofthe motor to be controlled. One

2,725,511 Patented Nov. 29, 1955.

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particular form of such control in which the present invention may bevembodied provides for regulation of reactive controls disposed in thesecondary simultaneously with the reactive control devices operativeupon the primary circuit of the motor, such simultaneous operationbeingQ carried on regardless of which of the alternate choices ofrotation is selected. l

It is still a further object of this invention to provide switchless`inductive or reactive regulation of an induction motor having `anexternal secondary circuit that provides for high torque during startingsimilar to a squirrel cage motor and for the insertion of impedancewithin the secondary circuit by smooth stepless operation to enhancespeed control under suitable load conditions.

These and other objects will appear in the description to follow. In thedescription reference is made to the accompanying drawing which forms aparthereof and in which there is shown by way of illustration and not oflimitation a form in which this invention maybe embodied. `l In thedrawing there is shown a circuit diagram of an induction motor controlsystem in which speed control and direction lof rotation may be had inaccordance with this invention. v

Referring now to the drawing, there is shown therein a conventionalthree phase slip ring induction motor 1 havinga stator 2 and a woundrotor 3. The necessary' power for operating the motor 1 is suppliedthrough the power mains 4, 5 and 6.

A terminal 7 of the motor 1 is connected by alead 8 with aconnectinglead 9 which joins with an end of each of the two reactor windings 10'and 11 mounted re# spectively upon saturation reactors 12 and 13. Theopposite ends of the windings 10 and 11 are joined by leads '14 and `15with the power mains 4 and 6 respectively. In this'wa'y-two alternativeadmission paths for the supply of current tothe terminal 7 are providedmaking it possible toestablish the equivalent of direct connection frommain 4 or 6 with the terminal 7. The saturation reactors 12 and 13 maybe constructed with a three legged magnetic frame having the windings 10and 11 each respectively divided to surround the two outsideflegs of itsassociated-reactor frame in a manner to 4have vthe re.- sultant uxescancel one anotherin the middle leg. This construction is well known 'inthe art and in myco-pending'application, Serial Number 588,685, thereare shown three legged reactors of this construction. Other reactors, tobe herein referred to and shown in the ldraw'- ing, maybe o f likeconstruction so as to`minimize`the transformer effects harmful tosources vof direct current joined to one of the windings of eachreactor.

In asimilar fashion terminal 16-of motor 1 is connected by lead 17 witha connecting lead 18 that joins with an end of each of the two reactorwindings 19 and 20.moun't ed respectively upon saturation reactors 21and 22. The opposite ends of the windings 19 and 20 are joined fre'-spectively by leads 23 and 24 with power mains 6 and '4 respectively.lIn this way alternative admission paths between the mains 6 and 4 andthe terminal 16 are provided.

A terminal 25 of the motor 1 is connected by a lead 26 to a connectinglead 27 that joins an end of each of the two windings 28 and 29 mountedrespectively on sat-uration reactors 30 and 31. The opposite ends of thewind-A ings 28 and 29 are joined together by a lead 32 which is in turnconnected by a lead33 with the powermain 5. While`tw`o -admission pathsare thus provided for theterminal 25 of the motor 1, the same are notValternative and are `confined to a single connection with the main 5 forpurposes to be 'more fully described hereinafter. The saturationreactors13, 31 and A22 are arranged toy be controlled by saturation coils 34, 35and 36, the same being connected in series and joined at one end bymeans of a lead 37 with one output terminal of a rectifier 38. Therectifier 38 is arranged to be supplied with alternating current by aninduction regulator winding 39 joined thereto by leads 40 and 41.

The winding 39 forms a part of an induction regulator 42 having an inputwinding 43 joined by leads 44 and 45 with the power mains 6 and 4respectively. The induction regulator 42 also has another output winding46 which is joined by leads 47 and 48 with the input terminals of arectifier 49.

The saturation reactors 12, 30 and 21 are controlled by saturationwindings 50, 51 and 52 which are connected in series and joined by alead 53 with one output terminal of the rectifier 49. The returnconnections for the saturation windings of the saturation reactors areprovided in a manner to be presently described.

In addition to the regulating means above described and associated incircuit with the primary or stator windings of the motor 1 regulatingelements in circuit with the secondary or rotor windings may also beemployed as illustrated in the drawing. As shown therein there areconnected with slip ring terminals 54, 55 and 56 secondary resistors 57,58 and 59 respectively. The resistors 57, 58 and 59 are joined at theirouter ends to one another by leads 60 and 61. In shunt relationship withthe resistors 57, 58 and 59 are impedance windings 62, 63 and 64respectively, the same being mounted upon and as part of saturationreactors 65, 66 and 67.

Saturation reactors 65, 66 and 67 are provided with saturation windings68, 69 and 70. The saturation windings 68, 69 and 70 are joined inseries and connected at one end by means of lead 71 and leads 72 and 73with the lower ends of the windings 36 and 52 respectively. In this waythe windings 68, 69 and 70 provide a return connection for all of theother saturation windings devoted to the control of the primary circuitof the motor 1, this being accomplished by a return lead 74 which joinsat one end with the winding 70 and at the opposite end with a crossconnecting lead 7S which is connected as shown to output terminals ofthe rectifiers 38 and 49. By reason of the unidirectional conductivityof the said rectifiers 38 and 49 the single return lead 74 is sutiicientfor the purpose as will be more fully explained hereinafter.

In normal operation at the outset the flux diverting arm 76 of theinduction regulator 42 will be in mid or vertical position and neitherof the windings 39 nor 46 will be excited. If the operator chooses todeiect the arm 76 to the position shown in the drawing winding 39becomes excited and the rectifier 38 becomes a source of direct currentpotential. When this occurs, saturation reactors 13, 31, 22, 65, 66 and67 become saturated and their corresponding reactor coils 11, 29, 20,62, 63 and 64 are deprived of their normally high impedance. Thispermits power to be admitted from the mains 4, and 6 to the terminals16, 2S and 7 respectively. The motor 1 being thus supplied with powertends to accelerate. At the outset of this acceleration there is littleimpedance in the windings 62, 63 and 64 by reason of the more or lesscomplete saturation of the magnetic material with which they areassociated. Large secondary currents are thus permitted to flow toprovide a large starting torque if desired and the motor 1 acceleratesand behaves in a manner comparable to that of a squirrel cage motor. Ifthe arm 76 of the induction regulator 42 were thrown to the extremeopposite position an entirely comparable situation would exist exceptthat the motor 1 would be driven in the opposite direction. Completereversability of the motor 1 without resort tov any switching is thusprovided.

If regulation of the output of the motor 1 is desired, the arm 76 of theregulator 42 is moved to an appropriate intermediate position betweenits mid positionY and the position shown. When this occurs, incompletesaturation of saturation reactors 13, 31, 21, 65 and 67 is provided andtheir corresponding reactor coils exhibit a corresponding impedance.This causes a limitation to be placed upon the voltage applied to theprimary windings of the motor 1 and furthermore at the outset ofacceleration there is interposed an equivalent resistance in thesecondary circuit somewhat less than the resistance of resistors 57, 58and S9. As acceleration of motor 1 progresses, the frequency ofsecondary current diminishes and without any alteration of the positionof the arm 76 the effect of secondary resistance diminishes accordingly.This permits the starting of motor 1 with a moderate inrush of startingcurrent and furthermore permits speed regulation of motor 1 steplesslyover a wide range.

Saturation reactors 30 and 31, while not essential to some of theobjectives to be accomplished, serve to maiu tain complete balance inthe primary circuit of motor 1 throughout the range of regulation ofpower input. They play no part, however, in the reversability functionwhich is performed entirely by the saturation reactors 12 and 21 on theone hand and 13 and 22 on the opposite hand. It is also possible todispense with the regulating circuit elements in the secondary circuitand to employ, if desired, a squirrel cage rotor in place of the woundrotor 3. In such an arrangement complete reversability is preserved andsome measure of speed control might also be obtained depending upon thecharacter of the load imposed upon the motor 1.

The secondary circuit of the apparatus shown in the drawing may also berearranged to cooperate with other well known speed regulatingarrangements, such as, cascading or concatenation arrangements eitherdirect or differential or both. For example, if the resistors 57, 5S and59 are replaced by or regarded as being the stator windings of asquirrel cage motor, the shaft of which is mechanically coupled with theshaft upon which rotor 3 is mounted, then a cascading system isestablished which calls for full speed operation when saturationreactors 65, 66 and 67 are excited and half speed operation when thesame are not excited. With such an arrangement it may be desirable tocontrol the excitation of saturation reactors 65, 66 and 67independently or semi-independently of the control of saturationreactors 13, 31, 22 and 12, 30, 21. This can be easily accomplished byproviding an additional variably supplied rectifier for furnishingexcitation current to the saturation reactors 65, 66 and 67. In likemanner other variable speed motor arrangements such as the spinner typemotor having an intermediate rotor may be steplessly regulated withoutresort to switches by application of the invention herein disclosed.

I claim:

l. In a reversible three phase induction motor the combinationcomprising a stator having three primary windings and three terminals, arotor, a first forward and a first reverse saturation reactor impedancewindings connected at one end of each to one another and to a firstterminal of said motor the opposite ends of said windings being adaptedfor connection respectively to a first and a second line of a threephase power supply, a second reverse and a second forward saturationreactor windings connected at one end of each to one another and to asecond terminal of said motor the opposite ends of said windings beingadapted for connection respectively to said first and second lines ofsaid three phase power supply, third forward and reverse saturationreactorwindings connected at one end of each to one another and to thethird terminal of said motor the opposite ends of said windings beingjoined and adapted for connection with the third line of said threephase power supply, said forward saturation reactor windings beingprovided with a set of magnetic field frames interlinking the same andsaid reverse saturation reactor windings being provided with a set ofmagnetic field frames interlinking the same distinct from the fieldframes of said for ward saturation reactor windings, forward excitationmeans including excitation windings interlinking said forward saturationreactor field frames adapted to alter the degree of saturation of thefields of said forward saturation reactors simultaneously, and reverseexcitation means including windings interlinking said reverse saturationreactor field frames adapted to alter the degree of saturation reactorssimultaneously, said excitation means being adapted to be activatedalternatively whereby phase sequence of current supplied to said motormay be inverted without unbalance of phase loading, there being furtherprovided as a source of excitation current for said forward and reverseexcitation means an inductive regulator having a field frame, a primarywinding adapted to be supplied with alternating current and forward andreverse secondary windings interlinking said field frame, a movable coremeans mounted on said field frame movable to establish coupling betweensaid primary winding and said forward secondary winding only when in oneposition and between said primary winding and said reverse secondarywinding only when in another position, a forward rectifier connected tosaid forward secondary winding to be supplied with current therefrom andconnected at its output with said forward excitation means, and areverse rectifier connected to said reverse secondary winding to besupplied with current therefrom and connected at its output to saidreverse excitation means.

2. 1n an apparatus in accordance with claim 1 wherein the motor rotor iswound providing a secondary motor circuit, saturation reactor meanshaving reactance windings in circuit with the secondary circuit of saidmotor and saturation windings, a connection joining one output terminalof the forward rectifier with an output terminal of like polarity of thereverse rectifier and joining the two said output terminals to one endof said saturation windings, and circuit means joining the remaining endof said saturation windings to the remaining output terminals of saidrectifers.

References Cited in the file of this patent UNITED STATES PATENTS808,944 Porter et al. Ian. 2, 1906 1,713,223 Green May 14, 19291,844,704 Thompson Feb. 9, 1932 1,955,322 Brown Apr. 17, 1934 2,228,078Gulliksen Ian. 7, 1941 2,379,146 Griscom June 26, 1945 2,384,864Wickerham Sept. 18, 1945 2,384,865 Wickerham Sept. 18, 1945 2,411,608Lesnick Nov. 26, 1946 2,440,319 Wickerham Apr. 27, 1948 2,559,538 JacobsJuly 3, 1951 2,676,292 Spencer Apr. 20, 1954

